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Just put (-2) as a possible "a" and do the work, it took me 30 sec to get to answer "A"

That's a valid approach.

"MUST BE TRUE" questions:These questions ask which of the following MUST be true, or which of the following is ALWAYS true for ALL valid sets of numbers you choose. Generally for such kind of questions if you can prove that a statement is NOT true for one particular valid set of numbers, it will mean that this statement is not always true and hence not a correct answer.

So, for "MUST BE TRUE" questions plug-in method is good to discard an option but not 100% sure thing to prove that an option is ALWAYS true.

As for "COULD BE TRUE" questions:The questions asking which of the following COULD be true are different: if you can prove that a statement is true for one particular set of numbers, it will mean that this statement could be true and hence is a correct answer.

So, for "COULD BE TRUE" questions plug-in method is fine to prove that an option could be true. But here, if for some set of numbers you'll see that an option is not true, it won't mean that there does not exist some other set which will make this option true.
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Now, 0 ≤ a ≤ 1 is NOT always true, because, a can be less than or equal to -1, say -2 ((-2)^5<-2), and in this case this option is not true.

Does this make sense?

I don't quite get it Bunuel. I mean it looks fine that when you pick -2 it satisfies the inequality on question stem and is not good for any of the statementsBUT, when one tries to find the range for a^5<=a, one ends up with 0<=a<=1, which is the exact same as option III

I'm pretty sure I'm getting the reasoning incorrectly

Please advice

Cheers!J

The trick here is more on the answer choices.

Look at I II and III. all are right (pick out some numbers).

Therefore I was totally confused because non of the answers had the right answer (I II and III)

I finally chose D, but hesitate between A and D quite a long time...

This is a tricky tricky question, since it takes into consideration that the answers are correct but they do not cover all the POSSIBLE answers.

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22 Nov 2015, 19:18

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